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    <title>ShellCheck: SC3019 – In POSIX sh, exponentials are undefined.</title>
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    <h1>SC3019 – ShellCheck Wiki</h1>
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    <h2 id="in-posix-sh-exponentials-are-undefined">In POSIX sh,
exponentials are undefined.</h2>
<h3 id="problematic-code">Problematic code:</h3>
<p>ShellCheck noticed you're using <code>**</code>-notation with two
asterisks to obtain an exponent's value. Some examples:</p>
<div class="sourceCode" id="cb1"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb1-1"><a href="SC3019.html#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="co">#!/bin/sh</span></span>
<span id="cb1-2"><a href="SC3019.html#cb1-2" aria-hidden="true" tabindex="-1"></a><span class="bu">echo</span> <span class="va">$((</span><span class="dv">2</span> <span class="op">**</span> <span class="dv">3</span><span class="va">))</span> <span class="co"># Using `**` for an exponent is undefined in POSIX sh.</span></span></code></pre></div>
<h3 id="correct-code">Correct code:</h3>
<p>Other possibilities exist:</p>
<div class="sourceCode" id="cb2"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb2-1"><a href="SC3019.html#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="co">#!/bin/sh</span></span>
<span id="cb2-2"><a href="SC3019.html#cb2-2" aria-hidden="true" tabindex="-1"></a><span class="bu">echo</span> <span class="va">$((</span><span class="dv">2</span> <span class="op">*</span> <span class="dv">2</span> <span class="op">*</span> <span class="dv">2</span><span class="va">))</span>   <span class="co"># equivalent to `bash`&#39;s `echo $((2 ** 3))`</span></span>
<span id="cb2-3"><a href="SC3019.html#cb2-3" aria-hidden="true" tabindex="-1"></a><span class="bu">echo</span> <span class="st">&#39;2 ^ 3&#39;</span> <span class="kw">|</span> <span class="fu">bc</span>     <span class="co"># piping the formula to `bc` to parse the output https://stackoverflow.com/a/13111995</span></span>
<span id="cb2-4"><a href="SC3019.html#cb2-4" aria-hidden="true" tabindex="-1"></a><span class="bu">printf</span> <span class="st">&#39;2 ^ 3\n&#39;</span> <span class="kw">|</span> <span class="fu">bc</span> <span class="co"># piping using `printf` (newline `\n` is mandatory)</span></span></code></pre></div>
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POSIX!</li>
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